invoke inner class method using outer class instance

Question

I have a class PersonStoryDerivedTest which has an inner class "InnerClass" which has function foo in it.

if I have only an instance a of PersonStoryDerivedTest, and dont have the class name/constructor/methods... and I want to invoke foo (I know it is the second method in hte inner class). how can I do it?

public class PersonStoryDerivedTest extends PersonStoryTest {

    private void thePersonRests(Integer hours) {
        person.rest(hours);
    }

    public void ff(String g){
        System.out.println("Alex");
    }

    public class InnerClass extends PersonStoryTest {
        public void aPerson(Integer age) {
            person = new Person(age);
        }

        public void foo(String g){
            System.out.println("David");
        }
    }
}

public class test {

    public static void main(String[] args) {

        PersonStoryDerivedTest a = new PersonStoryDerivedTest();
        Method[] g1 =  a.getClass().getDeclaredMethods();
        g1[1].invoke(a,"fff");   // print Alex (works well)

        PersonStoryDerivedTest.InnerClass ab = a.new InnerClass();
        Class<?>[] b = a.getClass().getDeclaredClasses(); 
        Method[] g =  b[0].getDeclaredMethods();
        g[1].invoke(ab,"fff"); // print David  (works well)
        g[1].invoke( b[0] ,"fff");   // (does not work... how can I create the appropriate instance     needed by only having b[0])
        }
}

thnx

possible duplicate of [How to test a class that has private methods, fields or inner classes](http://stackoverflow.com/questions/34571/how-to-test-a-class-that-has-private-methods-fields-or-inner-classes) — jruizaranguren, Dec 27 '14 at 17:17

score 0 · Answer 1 · answered Dec 27 '14 at 17:12

0

An outer class instance doesn't have a reference to an inner class instance. Only an inner class instance has a reference to an outer class instance. Multiple inner class instances can have a reference to the same outer class instance.

answered Dec 27 '14 at 17:12

user102008

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but I can get the inner class by: "Class>[] b = a.getClass().getDeclaredClasses();" – Atheel Massalha Dec 27 '14 at 17:15
1

The class is a static type structure. To call a method you need an instance of the class, not its type. – Gene Dec 27 '14 at 17:21
true.. but how can I create this instance using only an instance of the outter class + Reflection ? – Atheel Massalha Dec 27 '14 at 17:23

score 0 · Accepted Answer · edited May 23 '17 at 12:20

I think you want too much from reflection, see for example: Is it possible in java to create 'blank' instance of class without no-arg constructor using reflection?

The following works, but only if you add constructors to the classes. When there are no constructors, I could not get it working:

public class Person
{
    public Person(int age)
    {
        System.out.println("person with age " + age);
    }
    public void rest(int hours)
    {
        System.out.println("person rests " + hours);
    }
}

public class PersonStoryDerivedTest extends PersonStoryTest {
    public PersonStoryDerivedTest()
    {
        System.out.println("PersonStoryDerivedTest cnstr.");
    }
    private void thePersonRests(Integer hours) {
        person.rest(hours);
    }
    public void ff(String g){
        System.out.println("Alex");
    }

    public class InnerClass extends PersonStoryTest {
        public InnerClass() { System.out.println("InnerClass cnstr."); }
        public void aPerson(Integer age) {
            person = new Person(age);
        }

        public void foo(String g){
            System.out.println("David");
        }
    }
}

public class PersonStoryTest
{
    public PersonStoryTest()
    {
        System.out.println("PersonStoryTest cnstr.");
    }
    Person person;
}

import java.lang.reflect.*;
public class test {
public static void main(String[] args) throws Exception {
    PersonStoryDerivedTest a = new PersonStoryDerivedTest();
    Method[] g1 =  a.getClass().getDeclaredMethods();
    g1[1].invoke(a,"fff");   // print Alex (works well)

    PersonStoryDerivedTest.InnerClass ab = a.new InnerClass();
    Class<?>[] b = a.getClass().getDeclaredClasses(); 
    Method[] g =  b[0].getDeclaredMethods();
    g[1].invoke(ab,"fff"); // print David  (works well)
    Constructor<?>[] cs = b[0].getConstructors();
    Object o = cs[0].newInstance(a);
    g[1].invoke( o ,"fff");   // now works too... 
    }
}

prints output:

PersonStoryTest cnstr.
PersonStoryDerivedTest cnstr.
Alex
PersonStoryTest cnstr.
InnerClass cnstr.
David
PersonStoryTest cnstr.
InnerClass cnstr.
David

you are welcome, it's been fun. It appeared to me like an alchemy, but doing some search reveals this to be a popular topic: http://jroller.com/tomdz/entry/reflection_inner_classes http://stackoverflow.com/questions/728842/instantiating-an-inner-class and the list goes on... — Palo, Dec 28 '14 at 01:27

invoke inner class method using outer class instance

2 Answers2